If you're doing a Javascript-centric website, the back-end support is often “fairly light, anyway.” These days, it mostly consists of RPC-call handlers and a persistent session-store... and of course, queries from some SQL database or another.

The best approach is probably to map-out your intended site very carefully, then look over the various Perl-based offerings to find the one that gives you the most coverage at the least cost. This may or may not be (likely won't be...) a direct parallel to “the way that PHP does it.”